Lucien's efforts are seen by everyone.
And those thousands of Mermaids and Nagas who wanted to help him can't help but feel useless as they see that their best ranged attacks didn't really harm Tyrion.
Instead of aiding their King, they hindered him, and he ended up having to save them once again. Any leader could be upset and disappointed in his troops after such a disaster.
But instead of appearing upset, Lucien gives a quick, gentle smile to Saria and his troops.
The Mermaids can sense it, and the Naga can see in Lucien's eyes that he is not disappointed in them but grateful for their attempt, even with it failing.
"Huh???" Thousands of women are confused, but their hearts are filled with happiness.
Lucien can't divert his attention from Tyrion now, so he quickly refocuses on the battle, but that brief look is enough for Saria to understand that they need to retreat.